时效工艺对Ti-Ni-V形状记忆合金显微组织和超弹性的影响

Effect of aging process on microstructure and superelasticity of Ti-Ni-V shape memory alloy

采用TEM和拉伸实验研究经300、400和500℃分别时效0.5-100 h后,时效温度和时效时间对Ti-50.8Ni-0.5V(摩尔分数,%)形状记忆合金室温显微组织和超弹性(SE)的影响。结果表明,时效温度对合金析出相形貌和SE特性的影响比时效时间显著。随时效温度的升高,合金中Ti3Ni4析出物形态由颗粒状向针状再向粗片状演变,合金的应力诱发马氏体相变临界应力(σM)降低,SE特性变差。300℃时效态合金的σM最大,SE最好;500℃时效态合金的σM最小,SE最差。随时效时间的延长,300℃时效态合金的SE特性稳定,σM和超弹性能耗降低;400和500℃时效态合金的超弹性残余应变增加,SE特性逐渐消失。

The effects of aging temperature and aging time on the microstructure and superelasticity （SE） at room temperature of Ti-50.8Ni-0.5V （mole fraction, %） shape memory alloy aged at 300, 400 and 500℃ for 0.5 100 h, respectively, were investigated by TEM and tensile test. The results show that the effects of aging temperature on the precipitate morphology and SE property are more outstanding than those of aging time. With increasing aging temperature, the morphology of Ti3Ni4 precipitates in the alloy changes from the fine particle-shape to the needle-shape and then to the plate-shape; the critical stress for inducing martensitic transformation （σM） decreases; and the SE property becomes poor. The σM is the largest and the SE property is the best for the alloy aged at 300℃, and the σM is the smallest and the SE property is the worst for the alloy aged at 500℃. With increasing aging time, the SE property is stable, the σM and the superelasticity energy dissipation decrease for the alloy aged at 300℃; the residual strain of the superelasticity increases and SE property disappears gradually for the alloy aged at 400 and 500℃.